Its 15% thinner, scooped/lower front section for mastfoot pressure, slightly wider tail. I'd been out on my iS76/6.4 Warp today & the wind dropped off. I borrowed a friends Tush X15 7.7 then a 9m X15 (nice sails) that where already rigged as I did not have time to rig my on up as we only had 1-hour of day light. I used them on my iS111 2008, no problem with these combos. I bought the iS111 to use with Warps 7.8 & 9m and I wont be using smaller sails as the iS111 feels pretty big.
Cheers